1. Field of the Invention
The present invention relates to an optical system, in particular for a motor vehicle, such as a lighting and/or indicating device having in particular a photometric function that is useful when the vehicle is moving on the road, allowing the vehicle to be seen by other vehicles or allowing the driver of the vehicle to see outside.
2. Description of the Related Art
Conventional visual indicating or lighting systems for motor vehicles comprise a casing containing a point source of light such as a bulb and an optical system to focus the beam in a principal direction. The outer face of the casing can exhibit varied forms and can for example harmoniously extend the curves of the body, thereby contributing to the aesthetics of the vehicle.
These conventional systems emit light from a point source. Hence, optical devices have been developed to expand the surface area perceived as being the emission zone. However, these optical devices do not enable a homogeneous output of emission, regardless of the direction of observation, to be produced.
Now, for reasons of visibility of the vehicle and therefore safety, as well as for esthetic reasons, it is desirable to emit the light from a surface source and to provide a homogeneous visual output of this source regardless of the direction of observation.
Moreover, surface light sources, such as organic light-emitting diodes (OLEDs), are known. However, conventional OLEDs exhibit a luminance that is too low to be able to be used in an indicating or road lighting application. Typically, the luminance provided by conventional OLEDs is in the order of 1,000 Cd/m2, while 5,000 to 10,000 Cd/m2 would be needed to meet the photometric regulations regarding road indicating.
To address this drawback, modified OLEDs have been produced to markedly increase the directivity of emission of the OLED. The diagram of emission is hence non-Lambertian and the luminous flux is sent in a prioritized optical direction, thereby improving the luminance in this direction. For example, document FR 2 926 677, which is equivalent to U.S. Patent Publication 2011/0079772, which documents are incorporated herein by reference and made a part hereof, discloses an organic light-emitting diode device emitting a light beam exhibiting high directivity. Such an organic light-emitting diode comprises, between these two electrodes, various layers, in particular a light-emitting layer, a layer encouraging the transport of electrons up to the emitting layer and a layer encouraging the transport of holes up to the emitting layer. All these layers form a microcavity, the thickness of which is adjusted to create an optical resonance. The result of such a structure is an emission of a light beam exhibiting high directivity.
These modified OLEDs exhibit several particularly disadvantageous drawbacks. These organic light-emitting diodes today comprise small molecules, since they are the most efficient and more suited to producing an indicating function in a limited space, for example a vehicle rear wing. However, these molecules must be protected from water and oxygen molecules, and this is achieved using glass sheets. OLEDs used for performing an indicating function therefore comprise a protective glass sheet in contact with the emitting layer. The glass sheets highly restrict the possible forms of the organic light-emitting diodes. The OLEDs must therefore have flat surfaces or at most ruled surfaces, and they therefore cannot consist of a screen having any arbitrary kind of warped surface such as the present-day lens of a lighting and/or indicating device for a motor vehicle. This therefore raises design issues. Furthermore, the prioritized direction of emission of the beam is necessarily normal to the plane of the OLED. These limitations lead to tight constraints both on the form of the system including the OLED and on the orientation of the plate which must be normal to the prioritized optical direction. In practice, the field of application of these modified OLEDs is therefore a priori restricted.
To avoid these constraints of orientation and flatness of the plate, solutions have been developed to create an OLED on a flexible substrate. These OLEDs therefore provide a good freedom of choice concerning the form given to them. They can in particular exhibit a rounded or bent outer surface. They can consequently equip a vehicle to provide a good continuity of form between the body and the display system. However, the luminance of these flexible OLEDs remains relatively low and they are difficult to use, or even unusable, for passenger compartment lighting functions, and even less so for photometric functions such as indicating functions or lighting functions.
Therefore, a need exists to provide a system for emitting light from a surface zone with an improved luminance and a homogeneous output regardless of the direction of observation, while limiting the form constraints imposed on the system.